The invention relates to tensioners, more particularly to linear tensioners having damping of a pulley movement by linear bearings.
Most engines used for automobiles and the like include a number of belt driven accessory systems which are necessary for the proper operation of the vehicle. The accessory systems may include an alternator, air conditioner compressor and a power steering pump.
The accessory systems are generally mounted on a front surface of the engine. Each accessory has a pulley mounted on a shaft for receiving power from some form of belt drive. In early systems, each accessory was driven by a separate belt that ran between the accessory and the crankshaft. Due to improvements in belt technology, single serpentine belts are now generally used in most applications. A single serpentine belt routed among the various accessory components drives the accessories. The engine crankshaft drives the serpentine belt.
Since the serpentine belt must be routed to all accessories, it has generally become longer than its predecessors. To operate properly, the belt is installed with a pre-determined tension. As it operates, it stretches slightly over its length. This results in a decrease in belt tension, which may cause the belt to slip. Consequently, a belt tensioner is used to maintain the proper belt tension as the belt stretches during use.
As a belt tensioner operates, the running belt may excite oscillations in the tensioner spring. These oscillations are undesirable, as they cause premature wear of the belt and tensioner. Therefore, a damping mechanism is added to the tensioner to damp operational oscillations.
Various damping mechanisms have been developed. They include viscous fluid dampers, mechanisms based on frictional surfaces sliding or interaction with each other, and dampers using a series of interacting springs.
Representative of the art is U.S. Pat. No. 4,362,525 (1982) to Sproul that discloses a tensioner having a camming block that engages an angled surface on a base. As the tensioner arm moves the camming block moves against the angled surface having a frictional coefficient thereby providing a damping force on the arm.
The prior art tensioners are complex requiring several components. They also do not provide design flexibility by orienting components to take advantage of the mechanical relationship between the belt and the frictional components. Prior art tensioners also generally impart an arcuate motion to the pulley center. Finally, the prior art tensioners do not utilize linear damping bearings.
What is needed is a tensioner having a linear bearing. What is needed is a tensioner having a damping linear bearing. What is needed is a tensioner having frictional blocks that impart damping in response to linear movement of a pulley plate. What is needed is a tensioner having damping determined by a force couple acting on frictional blocks engaging a pulley plate. The present invention meets these needs.
The primary aspect of the invention is to provide a tensioner having a linear bearing.
Another aspect of the invention is to provide a tensioner having a damping linear bearing.
Another aspect of the invention is to provide a tensioner having frictional blocks that impart damping in response to linear movement of a pulley plate.
Another aspect of the invention is to provide a tensioner having damping determined by a force couple acting on frictional blocks engaging a pulley plate.
Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.
The invention comprises a tensioner having a base. A spring connected to the base biases a plate, having a pulley, toward a belt. Frictional blocks are aligned on the base in a staggered fashion along a spring centerline. The plate slidingly moves in a linear path between the blocks. The blocks constrain the path of the plate allowing movement in only a single axis generally parallel to a spring axis. A hubload from a belt running on the pulley combined with the spring force acting on the plate creates a force couple acting on the plate through the frictional blocks. The engaging surfaces between the plate and the blocks have a predetermined coefficient of friction thereby creating a damping force as the pulley and plate move in a linear path on the blocks.